Android网络连线之HttpURLConnection【从网页获取图片 demo】移动开发m046350041的博客-

从网页获取图片

效果是这样，下面是代码：

layout

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"      android:orientation="vertical"     android:layout_width="match_parent"     android:layout_height="match_parent" > <EditText         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:id="@+id/et_target"         android:text="https://bkimg.cdn.bcebos.com/pic/574e9258d109b3de43046931c3bf6c81800a4c34?x-bce-process=image/resize,m_lfit,w_500,h_500,limit_1" /> <Button         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:text="visualizer"         android:onClick="visualizer"/> <ImageView         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/iv_result" /> </LinearLayout> 

StreamUtility（把流写在文件上）

public class StreamUtility { public static void writeStream2File (InputStream in, File file) throws Exception {         FileOutputStream outputStream = new FileOutputStream(file); int len= -1; byte[] buffer = new byte[1024]; while ((len= in.read(buffer)) !=-1){             outputStream.write(buffer,0,len); }         outputStream.close();         in.close(); } } 

Mainactivity.java

因为子线程不能更新ui，这里有两种方法

1.线程之间通讯构建第三方，利用handler传给主线程再更新ui
2.用runonUIThread方法，直接在子线程更新ui

public class MainActivity extends AppCompatActivity { private EditText et_target; private ImageView iv_result; private Handler handler =new Handler(){ @Override public void handleMessage( Message msg) { switch (msg.what){ case RESPONSE_SUCCESS:                     Bitmap result = (Bitmap) msg.obj;                     iv_result.setImageBitmap(result); break; case RESPONSE_FAILED:                     Toast.makeText(MainActivity.this, "失败"+msg.arg1, Toast.LENGTH_SHORT).show(); break; case RESPONSE_EXCEPTION:                     Toast.makeText(MainActivity.this, "异常", Toast.LENGTH_SHORT).show(); break; } } }; private final int RESPONSE_SUCCESS=1; private final int RESPONSE_FAILED=2; private final int RESPONSE_EXCEPTION=3; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);         et_target = (EditText) findViewById(R.id.et_target);         iv_result = (ImageView) findViewById(R.id.iv_result); } public void visualizer(View view) { final String path = et_target.getText().toString().trim(); final File file = new File(getCacheDir(), Base64.encodeToString(path.getBytes(),Base64.DEFAULT));/*缓存cache*//*现在没产生文件，写名，开流时候才产生*/ /*base64应用原因 1.转换成的字符串没有特殊字符2.加密好的也是唯一的，不能重复3.加密后的固定长度*/ if (file.exists() && file.length()>0){             Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());             iv_result.setImageBitmap(bitmap);             System.out.println("-----------------cache"); return; } new Thread(){ @Override public void run() {                 HttpURLConnection connection = null; try {                     URL url = new URL(path);                      connection = (HttpURLConnection) url.openConnection();                     connection.setRequestMethod("GET");                     connection.setConnectTimeout(5000); int code = connection.getResponseCode(); if (code == 200){                         InputStream inputStream = connection.getInputStream();                         StreamUtility.writeStream2File(inputStream,file);/*把流写入file文件上*/ /*Message message = new Message();*//*new是最慢的*/ final Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());/*从本地拿，绝对路径*/                         System.out.println("-----------------newload"); runOnUiThread(new Runnable() { @Override public void run() {                                 iv_result.setImageBitmap(bitmap); } }); /*如果只更新ui用runOnUiThread，如果给主线程发数据只能用handler*/ /*iv_result.setImageBitmap(BitmapFactory.decodeStream(inputStream));*//*位图，容易崩溃*/ }else {                         Message msg = Message.obtain();                         msg.arg1=code;                         msg.what=RESPONSE_FAILED;                         handler.sendMessage(msg); } } catch (Exception e) {                     handler.sendEmptyMessage(RESPONSE_EXCEPTION);                     e.printStackTrace(); } finally { if (connection != null)                     connection.disconnect(); } } }.start(); } } 

最后在androidmanifest加上网络权限

 <uses-permission android:name="android.permission.INTERNET"/>